The present invention relates to a magnetic thin-film head for a recording medium that can be magnetized perpendicularly (vertically) having a magnetic conduction body which is applied to a nonmagnetic substrate, is of ring head-like shape and contains two magnet legs of which the end pole pieces facing the recording medium are arranged one behind the other as seen in the direction of motion of the head and having a predetermined small gap width from each other and having leg parts which are spaced farther than the gap width and defining a space therebetween through which the turns of a write/read coil winding extend. Such a magnetic head can be found, for instance, in European Patent No. 0,012,912Al.
The principle of vertical magnetization for the storage of information is generally known (see, for instance, "IEEE Transactions on Magnetics", vol. MAG-16, no. 1, January 1980, pages 71 to 76.) For this principle, which is frequently also called vertical magnetization, special recording media in the form of rigid magnetic storage discs, individual flexible discs (floppy discs) or magnetic tape are required. Such a recording medium comprises at least one magnetizable storage layer of predetermined thickness which contains a magnetically anisotropic material, particularly of a CoCr alloy. The axis of the so-called easy magnetization of this layer is directed perpendicularly to the surface of the medium. By means of a special magnetic head, the individual pieces of information can then be written in by appropriate magnetization of the storage layer along a track as bits in successive sections, also called cells or blocks. The bits have here a predetermined extent in the longitudinal direction of the track, also designated as wavelength. This extent can be substantially smaller than the limit which is set for storage according to the principle of longitudinal (horizontal) magnetization by the demagnetization. Thus, the information density in the recording media can be increased accordingly by vertical magnetization.
The magnetic write and read head known for the principle of longitudinal magnetization, i.e., heads with which the write as well as the read function can be executed, however, cannot be adopted directly for vertical magnetization. Although, if these heads are used, which generally have ring head-like shape, the flux arrangement desired for the principle of vertical magnetization to form a circuit closed as far as possible with low magnetic reluctance, can be achieved, it is difficult to generate a sufficiently strong write field in the vertical direction with high bit densities and correspondingly small gap width of the ring head.
Therefore, there is reason to develop special magnetic write/read heads for this principle of vertical magnetization. A magnetic head suited for this purpose such as can be found, for instance, in the above European Patent Application, comprises, for conducting the magnetic flux, a magnetic conduction body applied to a plane nonmagnetic substrate of, in particular, ring head-like shape. This conduction body consisting of magnetizable material comprises two magnet legs, of which the end pole pieces facing the recording medium are arranged one behind the other as seen in the direction of motion of the head, and at a predetermined small spacing, also called gap width. The region of the end pole pieces is followed by a region of the head, in which the magnet legs are brought to a larger mutual spacing. In this manner a sufficiently wide space is obtained between the two magnet legs, through which the turns of a write and read coil winding extend. The ring head-like shape of the conduction body is utilized for the write function as well as for the read function as a magnetic head.
The individual parts of this magnetic head are applied on a plane substrate by a thin-film technique. This technology is generally known for write/read heads (see, for instance, "Feinwerktechnik und Messtechnik", 88th year, no. 2, March 1980, pages 53 to 59, or "Siemens-Zeitschrift", vol. 52, no. 7, 1978, pages 434 to 437).
According to this technique, magnetic thin-film heads are made by applying on a plane substrate a sequence of numerous layers of magnetic material such as, for instance, NiFe, of insulating material such as SiO, as well as varnishes and electrically conductive material such as copper. The desired geometric design of these layers such as the formation of a flat arrangement of a coil winding for generating a write/read coil winding is accomplished, for instance, by photolithographic processes by first applying varnish layers, exposure via masks and then chemical structuring. Thereupon, the structure obtained is transferred by purely chemical etching methods or by plasma etching methods into the metal or insulating layer to be structured. Since these layers must be applied and structured on top of each other, overall heights of 10 to 20 .mu.m and more are obtained, depending on the shape of the head. With an increasing number of layers, however, the structuring becomes less accurate; the positioning accuracy of the respectively last mask to the lowest structured layer decreases. This is also the case if the successive masks are always adjusted relative to the first, lowest structure, and specifically, due to the adjustment tolerances and the continuously changing imaging conditions from layer to layer, even if they still can be corrected in part. This applies particularly to the so-called hard-contact method which, because of its otherwise high imaging fidelity and the possibility of imaging the very finest structure in the .mu.m range is generally used and in which the mask is in direct contact with the layer of varnish on the substrate (see, for instance, "Introduction to Microlithography", ACS Symposium, Series 219, Washington, 1983, especially pages 18 and 19). For manufacturing the magnetic head shown in the above European Patent application, the last operations, namely, the structuring of the outer magnet leg, which is further removed from the substrate and which opens into the narrow writing or reading pole end piece with a width of, for instance, 5 to 50 .mu.m, are particularly difficult, since this must be done from a height of about 10 .mu.m or more; for, the mask required for the structuring is always placed on the highest points. At this particularly critical point this leads to blurred images, undesirable structure deviations and to a lack of reproducibility and an accordingly high rejection rate.
A further problem arises from the fact that the lower magnet leg, i.e., the magnet leg facing the substrate, is reinforced by an additional layer several micrometers thick, of magnetic material in order thus to reduce the magnetic reluctance in the magnetic circuit of the magnetic conduction body and to thereby increase the efficiency of the entire magnetic head. With respect to the known magnetic head, it is therefore considered advantageous to bring this further reinforcing magnetic layer as close as possible to the tip of the magnetic head or the corresponding end pole piece. With this, however, the danger exists that magnetic lines of flux are short-circuited between the forward edge of the further magnetic layer and the outer upper magnet leg, and consequently the lines of flux do not emerge and are not conducted via the two end pole pieces serving as the write/read leg tips.